The two proposed the amendment late last year. But the issue is receiving renewed attention in light of GOP-leaning super PACs that are spending millions of dollars on ads this election season.

Mr. Bennet said most people can’t evaluate ads or know if their backers have an axe to grind. He said a 2010 Supreme Court ruling known as Citizens United that removed limits on corporate and union spending in elections has made matters worse.

YOUTUBE

Pelosi one-ups Colbert with satirical attack ad

House Minority Leader Nancy Pelosi upped the comedy ante Thursday on Stephen Colbert with a tongue-in-cheek “attack” ad on the faux conservative, who has formed a real super PAC to support a less-than-real bid for the Republican presidential nomination.

In the YouTube ad, the California Democrat calls for voters to support efforts to “Stop Colbert” — in part because “he doesn’t even like kittens” and has used his super PAC to “attack my friend Newt Gingrich.”

Mrs. Pelosi closes the satirical video with a serious pitch for the Disclose Act, legislation being introduced Thursday by the Democrats that would require super PACs to disclose their funding sources.

CAMPAIGN

Colorado Democrats fire intern who attacked Romney

DENVER — The college student accused of “glitter-bombing” Mitt Romney after the Colorado caucuses has been fired from his unpaid internship with state Senate Democrats.

A conservative-leaning blog, Colorado Peak Politics, first reported that Mr. Smith worked for state Senate Democrats and had been fired. Some gay activists have used “glitter-bombing” to protest politicians’ opposition to same-sex marriage.

Colorado Senate majority chief of staff John Cevette says Mr. Smith was terminated Thursday. He was interning as part of a course at the University of Colorado at Denver. Mr. Smith has said “glittering” Mr. Romney was worth it, but he worries he could be expelled from school.

House-Senate negotiations on extending jobless benefits and a 2 percentage point cut in the payroll tax remained stalled Thursday, despite a proposal in which Democrats urged a modest six-week cut in the maximum time unemployed workers can receive jobless benefits.

Democrats, however, rejected efforts by House conservatives to require beneficiaries to enroll in GED classes or permit states to require drug tests as conditions of getting unemployment.

The Democratic proposal would allow unemployed people to receive a maximum 93 weeks of benefits in states with the highest jobless rates, rather than the 99 weeks permitted now. Republicans want to cut 20 weeks from the maximum benefit, though as a practical matter, falling jobless rates mean the maximum benefit would drop to 59 weeks under their plan.

There’s still no progress on the central issue of finding budget cuts to finance a cut in Social Security payroll taxes. At the hearing earlier this week, Democrats came out against GOP plans to freeze federal workers’ pay and require higher income seniors to pay higher Medicare premiums.

But Democrats have yet to come forward, publicly or privately, with an alternative roster of deficit-cutting proposals to raise $160 billion or so in savings to pay for extending the payroll-tax cut and jobless benefits for the long-term unemployed, as well as preventing a 27 percent cut in Medicare payments to doctors required under an outdated funding formula.

HOUSE

Bill delays rail safety mandate for years

A long-sought safety feature that Congress required after a deadly 2008 rail crash would be delayed for five years under legislation the House is expected to take up next week.

Shortly after a train collision near Chatsworth, Calif., Congress required rail operators transporting passengers or toxic materials to install equipment by the end of 2015 that would automatically stop a train in danger of an accident.

Federal investigators cited the lack of such a safety system, referred to as positive train control, as a contributing factor in the Chatsworth crash that killed 25 people and injured more than 100.

But a House bill that would dictate the nation’s future transportation agenda pushes back the installment deadline five years. Rail industry officials say more time is needed to deal with the complexity and costs associated with installing and operating the equipment.

“It’s still really in the product development stage,” said Robert L. Healy Jr., vice president of government affairs for the American Public Transportation Association, a trade association for commuter rail operators. “There’s not only a dearth of technology but also expertise in terms of getting this installed.”

Rail industry officials have projected it would cost freight railroads nearly $6 billion to install the safety systems and that passenger railroads would spend another $2.4 billion. The federal government authorized up to $250 million over five years to help subsidize the costs, but so far has allocated $50 million specifically for the safety systems. Many commuter lines, meanwhile, are already struggling to keep up with existing maintenance needs.

Federal safety officials have voiced concerns about the proposed delay. Deborah A.P. Hersman, chairman of the National Transportation Safety Board, told Rep. Grace F. Napolitano, California Democrat, that the agency has investigated scores of accidents in recent decades that could have been prevented if positive train control systems had been installed.

OHIO

Biden touts economic resiliency at stop

COLUMBUS — Vice President Joseph R. Biden says he’s convinced America is better positioned than other nations to continue to lead the world’s economy — whether or not his boss is still in charge.

Mr. Biden touted the resiliency of the U.S. economy Thursday during remarks to the Ohio Newspaper Association.

He said the economy will continue to provide Americans with decent jobs for years to come whether or not he and President Obama are in office. And he said he’s convinced people are regaining confidence about the country’s ability to lead economically.

Mr. Biden said he believed that in the year 2020 or 2030, the U.S. would be “the single most vibrant economy in the world,” adding it is in the world’s interest that it is.